Rotation control device of working machine

ABSTRACT

In a neutral range preset, there are set a zone for stopping and holding a rotating body only by a mechanical brake, a zone for holding the body only by performing position holding control, and a zone for simultaneously exerting both effects, i.e., the effect of the mechanical brake and the effect of the holding control. On-the-spot holding torque generated when the position holding control is performed is stored. The higher of the on-the-spot holding torque stored and accelerating torque according to an operation amount of the body at a rotation starting time is set as electric motor torque for acceleration. When performing a pressing work including pressing a bucket against an object for work, torque control is carried out according to the operation amount.

TECHNICAL FIELD

The present invention relates to a rotation control device for a workingmachine, such as an excavator, a crane, or the like, for rotatablydriving a rotating body by an electric motor.

BACKGROUND OF THE INVENTION

Taking an excavator as an example, the prior art associated therewithwill be described below.

The excavator generally employs a hydraulic motor driving system that isdesigned to use a hydraulic motor as a rotation driving source and todrive this hydraulic motor by discharge oil from a hydraulic pump.

In the case of employing this system, the discharge oil has itsdirection, pressure, and flow rate controlled by a control valvedisposed between the hydraulic pump and the hydraulic motor, so that theoperating direction, force, and speed of the hydraulic motor arecontrolled.

This system, however, has a drawback that a large amount of hydraulicenergy has to be squeezed and disposed of by the control valve,resulting in huge loss of energy.

Thus, an electric motor driving system has been proposed that employs anelectric motor as the rotation driving source (see Japanese UnexaminedPatent Publication No. 11-93210, for example).

Conventionally, a large electric excavator for a climbing crane or formining also employs the electric motor driving system in a rotationoperation.

In such an electric motor rotation driving system, the direction andspeed of rotation of a rotating body is controlled by adjusting therotation direction and rotating speed of the electric motor, therebysignificantly improving energy efficiency.

At the same time, when employing this system, a feedback speed controlsystem is normally used to control the speed of the rotating body suchthat a deviation between an actually measured speed of the rotating bodyand a target speed thereof corresponding to an operation amount of anoperation means is eliminated.

This system, however, has the following drawback concerning operationalperformance in rotation.

When the operation means is located in a neutral position and acommanded speed equals zero, braking torque is produced to stop arotating body. Once a rotating speed of the electric motor becomes zero,torque (stopping and holding force) that causes the zero speed to bemaintained will never be outputted, which results in the fact thatbraking and holding effect cannot be surely obtained.

For this reason, as a control system for stopping and holding the bodyis proposed another system that employs a mechanical brake mounted on aworking machine with a hydraulic driving system.

The mechanical brake, however, is basically designed to actuate as aparking brake when the rotating body is in a stopped state. If thisbrake is used as a means for decelerating and stopping the electricmotor in the electric motor rotation driving system withoutmodification, there arises a problem that brake wearing becomes severe,while the jerky movement of the rotating body is caused due to shocksfrom an on/off operation of the brake when decelerating andaccelerating, so that a smooth rotation stopping/accelerating effectcannot be obtained, thus degrading its operability.

On the other hand, in a normal operation of rotating an upper rotatingbody 2 above ground, a feedback speed control system enables control ofrotating speed according to the operation amount of the operation means,which has no operational problem.

In contrast, when performing a pressing work which involves excavatingearth by a bucket 6 and pressing its side against a wall surface g1 in agroove g to form the pressed wall surface g1, as shown in FIG. 14, thespeed of rotation around a rotating shaft ο becomes appropriate zero.Under the feedback speed control, a deviation between a target value ofthe rotating speed and an actually measured value thereof is increased.As a result, the feedback effect causes maximum rotation torque(electric motor torque) even when a slight amount of bucket operation istaken.

For this reason, when performing such a pressing work through therotation, the torque control carried out by an operator becomesimpossible, thereby impairing the machine operability.

Therefore, it is desirable that the feedback speed control system isemployed, while imposing a limitation on torque depending on theoperation amount.

When imposing the limitation on the torque as described above, the smalloperation amount of the operation means results in small torque of theelectric motor. Therefore, when the rotating body starts to rotatetoward an upper end side of an inclined ground or when the rotating bodystarts to rotate upwind under strong wind, the torque limitation asdescribed above produces a shortage of accelerating torque. This causesthe rotating body to rotate in a reverse direction, i.e. so-called“retrograde motion”, disadvantageously leading to degradation in itssecurity and operability.

Accordingly, the present invention is to solve the foregoing problems,and it is an object of the present invention to provide a rotationcontrol device for a working machine with improved operability inrotation.

Concretely, it is a first object of the invention to securely hold therotating body in a stopped state, to smoothly carry out a deceleratingand stopping function of the rotation and an accelerating effect thereofwithout energy loss for stopping and holding the body, and to make itpossible to use a known mechanical brake as it is.

It is a second object of the invention to prevent retrograde motion ofthe rotating body, which might be caused due to the shortage of torque,while imposing a limitation on the torque.

It is a third object of the invention to enable rotating torque controlin the pressing work.

DISCLOSURE OF THE INVENTION

To solve the foregoing problems, the present invention employs thefollowing arrangement.

According to one aspect of the present invention, there is provided arotation control device for a working machine that comprises an electricmotor for rotatably driving a rotating body, operation means for issuinga rotation command for rotation, control means for controlling theelectric motor based on the rotation command issued from the operationmeans, rotating speed detecting means for detecting a rotating speed ofthe rotating body, and a mechanical brake for generating mechanicalbraking force, wherein the control means has a neutral range set byadding a predetermined width to an absolute neutral point serving as abasic point, the absolute neutral point corresponding to an operationamount of the operation means of zero, and in the neutral range, amechanical brake zone is set on the absolute neutral point side, while aposition holding control zone is set on a side opposite to the neutralpoint side, and wherein the control means is adapted to cause themechanical brake to work in the mechanical brake zone of the neutralrange, to perform position holding control in the position holdingcontrol zone, thereby stopping and holding the rotating body, and toperform speed control according to the operation amount of the operationmeans outside the neutral range.

According to another aspect of the present invention, there is provideda rotation control device for a working machine that comprises anelectric motor for rotatably driving a rotating body, operation meansfor issuing a rotation command for rotation, control means forcontrolling the electric motor based on the rotation command issued fromthe operation means, and rotating speed detecting means for detecting arotating speed of the rotating body, the control means performing speedcontrol according to an operation amount of the operation means andimposing a limitation on a maximum value of accelerating torqueaccording to the operation amount, wherein, when the operation means ispositioned within a preset neutral range, the control means is adaptedto perform position holding control of the rotating body, to storetorque generated in the electric motor at this time as on-the-spotholding torque, and to set, in accelerating the rotation, the higher ofthe on-the-spot holding torque stored and the accelerating torqueproduced according to the operating amount of the operation means, aselectric motor torque for accelerating.

According to a further aspect of the present invention, there isprovided a rotation control device for a working machine that comprisesan electric motor for rotatably driving a rotating body, operation meansfor issuing a rotation command for rotation, control means forcontrolling the electric motor based on the rotation command issued fromthe operation means, and rotating speed detecting means for detecting arotating speed of the rotating body, the control means performing speedcontrol according to an operation amount of the operation means,wherein, when performing a pressing work including pressing a part ofthe rotating body against an object of work, the control means performstorque control according to the operation amount of said operation meansinstead of the speed control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of the entire configuration of an excavator onwhich a control device according to a first embodiment of the inventionis mounted, and of the arrangement of devices therein;

FIG. 2 is a block configuration diagram of the control device accordingto the first preferred embodiment;

FIG. 3 is a diagram showing a lever operation amount-target value ofspeed characteristic of the device;

FIG. 4 is an explanatory diagram of detailed settings of a lever neutralrange shown in the characteristic of FIG. 3;

FIG. 5 shows a relationship among an operation amount, a rotationaccelerating torque, and a rotation decelerating torque in a controldevice according to a second preferred embodiment of the invention;

FIG. 6 is a block configuration diagram of a control device according toa third embodiment of the present invention;

FIG. 7 is a flow diagram of speed feedback control carried out by thedevice;

FIG. 8 shows a relationship between a lever operation amount and atarget value of speed in the feedback control;

FIG. 9 is a flowchart for explaining an action of the device;

FIG. 10 is a flow diagram of torque control in the feedback control;

FIG. 11 shows a relationship between a lever operation amount and atarget value of torque in the control;

FIG. 12 is a flow diagram of speed control with a torque limitationperformed by a control device according to a fourth embodiment of thepresent invention;

FIG. 13 is a flowchart for explaining an action of a control deviceaccording to a fifth embodiment of the present invention; and

FIG. 14 is a front view showing a condition in which a bucket of theexcavator is pressed against an inner wall surface of a groove.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

Although some preferred embodiments of the present invention will bedescribed hereinafter in detail by taking an excavator as an appliedobject, the invention is not limited thereto. For example, the inventioncan be widely applied to a rotation type work machine, such as adeep-hole digging machine consisting principally of an excavator, acrusher, a crane.

First Embodiment (see FIGS. 1 to 4)

FIG. 1 illustrates the schematic configuration of an entire excavatorand the arrangement of devices therein, and FIG. 2 the blockconfiguration of a drive and control system.

As shown in FIG. 1, on a crawler type lower traveling body 1 isrotatably mounted on an upper traveling body 2, which is equipped withan excavating attachment 3. The excavating attachment 3 includes a boom4, an arm 5, a bucket 6, a boom cylinder 7, an arm cylinder 8, and abucket cylinder 9.

The lower traveling body 1 includes left and right crawlers 10L and 10R,which are rotatably driven and traveled by traveling motors 11L and 11Rand reduction gears 12L and 12R, respectively.

On the upper rotating body 2 are mounted an engine 13, a hydraulic pump14, a generator 15, the pump and generator being driven by this engine13, a battery 16, an electric motor for rotation 17, and a deceleratingmechanism for rotation 18.

As shown in FIG. 2, discharge oil from the hydraulic pump 14 is suppliedto the cylinders 7, 8 and 9 for the boom, arm and bucket, respectively,and to the left and right traveling motors 11L and 11R, via respectivecontrol valves 19, 20, 21, 22 and 23, by which an actuation or operationof the rotating body is controlled.

The generator 15 has driving force of the engine given thereto via anaccelerating mechanism 24 to generate power. The power generated by thegenerator 15 is partially charged in the battery 16 via a control device25 for controlling voltage and current, while the remaining power isgiven to the rotation electric motor 17 via an inverter 26, which is apart of control means.

A mechanical brake 27 serving as a negative brake for generatingmechanical braking force is provided in the rotation electric motor 17.With this mechanical brake 27 released, rotational force of the rotationelectric motor 17 is transmitted to the upper rotating body 2 via therotation decelerating mechanism 18 to rotate the upper rotating body 2leftward or rightward.

Reference numeral 28 denotes a rotation operating unit (for example, apotentiometer) serving as rotation operation means, which is operated bya lever 28 a. A command signal responsive to the operation amount of theoperating unit is inputted into a controller 29 which is a part ofcontrol means.

Furthermore, as sensors are provided a speed sensor 30 for detecting arotating speed (rotating speed) of the rotation electric motor 17, and aposition sensor (for example, encoder) 31 for detecting the position ofthe upper rotating body 2 with a rotation stopping place of the upperrotating body 2 set as zero point. Signals from both sensors 30 and 31are inputted as control data into the controller 29 via the inverter 26.

The controller 29 has a neutral range N previously set by addingpredetermined widths (for example, a tilt angle of the operating lever28 a of 7.5 degree in each of the leftward and rightward directions) inleftward and rightward directions of rotation, respectively, to anabsolute neutral point ο serving as a basic point where an operationamount of the rotation operating unit 28 (hereinafter referred to as“lever operation amount”) is zero, as shown in FIG. 3. When the lever ismoved or pushed down beyond the neutral range N, speed control iscarried out based on characteristics of the controller as shown in thefigure. When the lever exists within the neutral range N, switchingbetween control modes is performed according to the lever operatingamount, as shown in FIG. 4.

That is, in the neutral range N, a mechanical brake zone B where themechanical brake 27 exerts a braking effect is set within an inner sidearea thereof including the absolute neutral point ο. In contrast, withinthe outer side area respective to the brake zone in the neutral range Nis set a position holding control zone A where position holding control(in other words, servo lock control, that is, control for holding therotating body 2 on the spot based on a signal from the position sensor31) is carried out.

Both zones B and A, as shown in the figure, are set so as to bepartially superimposed on each other in a simultaneous use zone C, whereboth functions of the mechanical brake and the position holding controlare simultaneously carried out.

In FIG. 4, reference symbols LnL and LnR denote neutral identifyingpoints located on the extreme left and right of the neutral range N todefine the range from both leftward and rightward directions ofrotation.

Reference symbols LbL and LbR denote mechanical brake identifying pointslocated at a starting point and at an endpoint of the mechanical brakezone B. Reference symbols LzL and LzR denote position-holding-controlidentifying points located at a starting point and at an endpoint of theposition holding control, respectively.

Based on the foregoing settings, the electric motor 17 for rotation willbe controlled by the controller 29 and the inverter 26 in the followingmanner.

In Accelerating Rotation

When the lever operation amount reaches the mechanical brake zone B ofFIG. 4, the mechanical brake 27 is actuated, so that its mechanicalbraking force only holds the rotating body 2 in a stopped state.

Then, when the lever operation amount reaches the simultaneous use zoneC located at the boundary between the mechanical brake zone B and theposition holding control zone A, the position holding control starts towork, whereby the mechanical braking force and the position holdingcontrol effect are exerted to stop and hold the rotating body 2.

After the lever operation amount exceeds the simultaneous use zone C,the mechanical brake 27 is released, and the only position holdingcontrol is performed, thereby to hold the rotating body 2 on the spot byits position holding control effect.

Furthermore, when the lever operation amount exceeds the positionholding control zone A (neutral range N), the position holding controlis turned off, and the rotation electric motor 17 is rotated with itsspeed being controlled, based on its characteristics as shown in FIG. 3,thereby performing acceleration of its rotation.

Thus, since the mechanical brake 27 works when the rotating body is inthe stopped state, current to hold the body on the spot does not need tobe constantly passed through the rotation electric motor 17, whichcurrent might be necessary in the case of stopping and holding the bodyonly by the position holding control, thereby achieving energy savings.

Additionally, in a boundary of the speed control range (i.e. positionholding control zone A), the position holding control enableselimination of shocks caused by turning the mechanical brake off whenaccelerating the rotation, which shock might occur in the case ofstopping and holding the rotating body only by the mechanical brake 27,whereby a smooth accelerating effect can be obtained.

The simultaneous use zone C where both the position holding controleffect and the mechanical brake 27 function are simultaneously exertedis previously set, thereby smoothly switching from the mechanical brakeeffect to the position holding control in accelerating, and also fromthe position holding control, which will be described below, to themechanical brake effect in decelerating without shocks.

In Decelerating Rotation

When the operating lever 28 a returns to the neutral range N from arotation command position which is located outside the neutral range Nand enters or is moved to the position holding control zone A, controlfor decelerating and stopping is started.

At this time, if a rotating speed actually detected by the speed sensor30 falls below the position-holding-control starting speed previouslyset by the controller 29, the position holding control becomeseffective, which generates braking torque in the electric motor 17.

Thus, since the position holding control is started with the rotatingbody being sufficiently decelerated, there is no risk that large brakingtorque could be exerted by the position holding control under acondition of insufficient deceleration to cause excessive current topass through the rotation electric motor 17, thus leading to damage inthe electric motor 17 and a circuit.

Then, when the lever operation amount reaches the mechanical brake zoneB and the following conditions (1) and (2) are satisfied, the mechanicalbrake 27 is actuated to stop and hold the rotating body 2.

(1) The actually detected-rotating speed is equal to or less than apreset brake actuation speed.

(2) This condition, i.e. the condition in which the rotating speed isequal to or less than the brake actuation speed, continues for a setperiod of time.

Conversely, even when the lever operating amount reaches the mechanicalbrake zone B, if the above-mentioned conditions (1) and (2) are notsatisfied, the mechanical brake 27 remains being released, causing theonly position holding control to work, as shown in the center of a lowersection of FIG. 4.

Thus, during decelerating the rotation, even if the lever operationamount reaches the mechanical brake zone B, the mechanical brake 27 isnot actuated quickly. That is, the mechanical brake 27 is not actuateduntil the lever operation amount reaches the mechanical brake zone B andthe condition in which the rotating speed is equal to or less than thepreset speed (for example, speed of zero) continues for a while. Withthis arrangement, when the working machine repeatedly carries out worksincluding rotation, stopping, and rotation in succession, for example,when the working machine excavates earth and sand at one spot to scoopup them and rotates so as to load the scooped ones into a dump truck,wearing of the mechanical brake 27 and occurrence of shocks due to thebraking are prevented to obtain a smooth operation.

Second Embodiment (see FIGS. 1, 2, and 5)

In the first embodiment, speed control is carried out depending on theamount of lever operation outside the neutral range N, while, in thesecond embodiment, speed control with torque limitations is carried outoutside the neutral range N.

The configuration of the second embodiment is apparently the same asthat of the first embodiment. Note that these embodiments differ fromeach other only in the contents of control performed by the controller29 and the inverter 26. Thus, FIGS. 1 and 2 are cited, and in additionthereto FIG. 5 is used to explain the detailed contents of the control.

In Accelerating Rotation

Within the neutral range N, control of the second embodiment is the sameas that of the first embodiment. When the lever operation amount exceedsthe simultaneous use zone C, the mechanical brake 27 is released therebyto perform the only position holding control, an effect of which holdsthe rotating body 2 on the spot.

At this time, torque generated in the electric motor 17 (on-the-spotholding torque) is stored in the controller 29 via the inverter 26. Itshould be noted that the on-the-spot holding torque may reach themaximum torque Tmax of the electric motor 17. FIG. 5 illustrates a casewhere the on-the-spot holding torque reaches a level of the maximumtorque Tmax of the electric motor.

When the lever operation amount exceeds the position holding controlzone A (neutral range N), accelerating torque (a maximum value of theaccelerating torque) according to the lever operation amount shown inFIG. 5 is compared with the above-mentioned on-the-spot holding torquestored by the controller 29. The higher of the accelerating torque andthe on-the-spot holding torque is set as electric motor torque foracceleration, which causes the rotating body 2 to be rotatably driven.

That is, feedback speed control with a torque limitation that regardsthe above-mentioned set torque as the maximum value causes the electricmotor 17 to rotate.

Thus, in accelerating the rotation, as the electric motor torque foracceleration is set torque equal to or higher than the on-the-spotholding torque actually generated just before rotation starting time.This surely prevents the rotating body 2 from rotating in a reversedirection, i.e. the so-called “retrograde motion” which might occur dueto a shortage of torque, especially when the rotating body starts torotate toward an upper end side of an inclined ground or when therotating body starts to rotate upwind under strong wind.

In Decelerating Rotation

When the operating lever 28 a is returned from the rotation commandposition outside the neutral range N of FIG. 5 toward the neutral rangeN in decelerating, braking torque is calculated according to the leveroperation amount based on braking torque characteristics of FIG. 5. Thehigher of the braking torque calculated and the on-the-spot holdingtorque stored in the controller 29 at the rotation starting time asdescribed above is set as electric motor torque for deceleration, andthen by this set torque, the rotating body 2 is decelerated.

Thus, even when the rotating body stops rotation on the inclined ground,the electric motor torque is constantly proportional to the gravity.There is no risk that the braking torque could be inferior to thegravity, causing the rotating body 2 to retrograde toward a lower endside.

Note that when the lever returns to the neutral range N of FIG. 5 andits operating amount reaches the position holding control zone A, theposition holding control is started. Thereafter, when it reaches themechanical brake zone B, the mechanical brake 27 is engaged or actuatedto stop and hold the rotating body 2.

Starting of the position holding control restores the on-the-spotholding torque stored upon starting the rotation, to an initial value soas to prepare for update thereof to a next value to be stored.

Therefore, even if conditions including a tilt degree of the inclinedground, the weight of the rotating body, which depends on the presenceor absence of loads, are varied every time the rotation is stopped,since the on-the-spot holding torque responsive to the condition isnewly stored, the retrograde motion of the rotating body 2 is surelyprevented when accelerating and decelerating the rotation.

Although, in the above-mentioned first and second embodiments, theso-called “parallel” type excavator is taken as an example in whichelectricity is used as power for rotation and oil hydraulics are used aspower for other operations, the invention may also be applied to theso-called “series” type excavator that employs electric power as powersources for all actuators.

In the second embodiment, an example is taken in which both functions ofthe position holding control and the mechanical brake effect stops andholds the rotating body 2 within the neutral range N. When the speedcontrol with torque limitations are performed outside the neutral rangeas described above, the invention may also be applied to the case wherethe rotating body 2 is stopped and held only by the position holdingcontrol.

Third Embodiment (see FIGS. 6 to 11)

FIG. 6 illustrates the entire configuration of such a rotation controldevice according to the third embodiment.

In the figure, reference numeral 32 denotes a rotation operating portion(which is identical to the rotation operating portion 28 of FIG. 2, forexample, potentiometer) serving as the rotation operating means. Thisrotation operating portion 32 is operated by a lever 32 a. A commandsignal responsive to the amount of its operation is inputted into thecontroller 33 serving as the control means.

Reference numeral 34 denotes an engine, and reference numeral 35 agenerator 35 driven by this engine 34. Power from this generator 35 istransmitted to a rotation electric motor 38 via an inverter for thegenerator 36 and an inverter for the electric motor 37. Rotational forceof the rotation electric motor 38 is transmitted to the upper rotatingbody 2 via a reduction gear 39, causing the rotating body 2 to rotatearound a rotating axis.

Reference numeral 40 denotes an encoder serving as rotating speeddetecting means for detecting the rotating speed of the rotationelectric motor 38. The rotating speed of the electric motor detected bythis encoder 40 is inputted into the controller 33 as an actuallydetected rotating speed.

It should be noted that not only the generator 35, but also a battery 41and a capacitor 42 are provided as power sources of the rotationelectric motor 38. Any appropriate one of these sources may be selectedand used. Alternatively, these sources may be used in combination.Instead of such inner power sources, power may be supplied from an outerpower source. Reference numeral 43 denotes an inverter for battery, andreference numeral 44 an inverter for capacitor.

A hydraulic pump 46 is provided as a hydraulic source for a hydraulicactuator circuit 45 for driving hydraulic actuators, such as cylinders7, 8, and 9 of the excavating attachment 3. This hydraulic pump 46 isdriven by an electric motor for the pump 47. Reference numeral 48denotes an inverter for the pump electric motor.

The controller 33 controls speed of the rotation electric motor 38 bycarrying out the speed PID feedback control shown in FIG. 7 when thebody is freely rotated.

That is, the lever operation amount S is inputted into the controller 33in the form of a signal indicative of the operation amount, whereby atarget value of rotating speed ωref is calculated according to the leveroperation amount S by this controller 33.

This target value ωref is compared with an actually value ωs of therotating speed detected by the encoder 40 to obtain a deviationtherebetween. By the PID feedback control, a signal that intends torender the deviation (ωref−ωs) zero is transmitted to the electric motor38 via the inverter for the electric motor 37.

Thus, as shown in FIG. 8, the upper rotating body 2 rotates at a speedresponsive to the lever operation amount S. In FIG. 8, Sc is an actuatedposition where the upper rotating body 2 starts to be actuated.

For convenience, although, in FIG. 7, output from the encoder 40 isrepresented as the actually measured value of rotating speed ωs, in factthe rotating speed of the electric motor is detected by the encoder 40,and then the detected speed is divided by a reduction ratio of thereduction gear 39 to obtain the rotating speed ωs.

On the other hands, when performing a pressing work as shown in FIG. 14,torque control is carried out.

That is, the steps for determining the presence or absence of thepressing work are as follows. The lever operation amount S and arotation starting point Sc are compared with each other every controlcycle b as shown in FIG. 9 by the controller 33 (step S1, and S2). Atthe same time, the actually measured value of the rotating speed ωs anda threshold value ωe previously set as a minute value near zero as shownin FIG. 8 are compared with each other (step S3). When the leveroperation amount S exceeds the rotation starting point Sc and theactually measured value of the rotating speed ωs is smaller than thethreshold value ωe (Yes in steps S2 and S3), the condition of thepressing work is recognized, and then switchover to the torque controlis automatically done (step S4). At a step S5, a control cycle b isupdated, and the operation returns to the step 1. Note that, in the caseof “NO” in the step S2 or S3 (S<Sc or ωs>ωe), the feedback speed controlis carried out (step S6) as shown in FIGS. 7 and 8(step S6) to bringabout free rotation.

Note that, when an object to be subjected to the pressing work hasirregularities or is made of a soft substance, the rotating speed oftenbecomes above zero upon performing the pressing work. This rendersdetermination of the pressing work as mentioned above unstable, causinghunting. In this case, there may be preferably provided huntingpreventing mean for preventing hunting by decreasing feedback gains forthe speed control or by giving a time-lag to the changeover of theabove-mentioned determination.

In torque control, as shown in FIGS. 10 and 11, a target value torque rref as target value of torque is calculated from an operationamount-torque map 49 which sets a relationship between the leveroperation amount S and the target torque value τ ref. This torque valuecalculated is converted into a target current value ωref as a targetvalue of current, so that the torque PID feedback control is carriedout.

Thus, the presence of the pressing work is automatically recognized toperform the switchover to the torque control. By this torque control,the electric motor torque responsive to the lever operation amount S isobtained as shown in FIG. 11, whereby the pressing torque can becontrolled according to operator's intention (the lever operationamount).

In this control system, when the lever 32 a is pushed down from a leverneutral condition or position where its rotating speed is zero, to aposition slightly deeper than a starting point of rotation Sc of FIG.11, since the speed of the rotating body 2 is zero due to its inertial,the torque control is automatically started even when the body is in afreely rotating condition.

In this device, as shown in FIG. 11, the target torque value τ ref atthe starting point Sc is set to a value τ c larger than zero.

With this arrangement, at the starting point Sc, the rotation torque τ cstarts to work. Especially, as described above, when the lever 32 a ismoved to the deeper position than the starting point Sc, the rotationoperation is promptly started, and the actual measured value of speed ωsreaches the target value ωre, which results in the switchover to thespeed feedback control. This can improve speed controllability whenstarting the motion.

Fourth and Fifth Embodiments (see FIGS. 12 and 13)

The fourth and fifth embodiments are modifications of the thirdpreferred embodiment. The different points from the third embodimentwill only be described below.

In the fourth embodiment, in freely rotating, the speed feedback controlaccording to the flowchart of FIG. 1 is carried out in the same manneras the third embodiment. In the pressing work, the control (speedcontrol with torque limitation) is performed that imposes a torquelimitation according to the lever operation amount S on the speedfeedback control, based on the lever operation amount-torque limitingvalue map 50 preset, as shown in FIG. 12.

In the map 50 of FIG. 12, a sign τ lim on a vertical axis is a torquelimiting value.

Accordingly, the speed control with the torque limitation in thepressing work can provide the electric motor torque according to thelever operation amount in the same way as the torque control shown inFIGS. 10 and 11, thereby improving the operability when performing thepressing work as is the case with the third embodiment.

It should be noted that also in the fourth and next fifth embodiments,the torque limiting value τ lim at the starting point Sc is set to avalue τ c larger than zero, thereby improving the speed controllabilitywhen starting the motion as is the case with the third embodiment.

In the preferred embodiment, as shown in FIG. 13, when the actuallymeasured value of speed ωs is smaller than the target value ωref, thiscondition is recognized as the so-called powering condition, and then inthis powering condition, the speed feedback control is switched toanother speed feedback control with the torque limitation.

In detail, the target speed value O)ref is compared with the actuallymeasured one ωs every control cycle b (steps S11 and S12). If ωref<ωs,the normal speed feedback control is carried out (step S13).

On the other hand, if ωref>ωs (YES in the step S12), the poweringcondition is recognized, and then the normal speed feedback control isautomatically switched to another speed feedback control with the torquelimitation as described in the fourth embodiment (see FIG. 12) (stepS14). At a step S15, the control cycle b is updated to b+1 and theoperation returns to the step S11.

Therefore, in the pressing work, which is one of powering conditions,the electric motor torque is controlled by the torque limitation effectas is the case with the fourth embodiment.

In this control system, even in accelerating of free rotation, the speedcontrol effect with the torque limitation is exerted under the conditionwhere the actually measured value of rotating speed ωs is smaller thanthe target value ωref. This restricts the acceleration of the body,thereby eliminating the shocks occurring upon accelerating.

Additionally, in deceleration, the torque limitation is not imposed.This enables deceleration at the maximum torque, especially emergencystop.

Therefore, in view of these aspects, the operability is improved.

Note that, although, in the third and fourth preferred embodiments, thepressing work is automatically recognized, thereby switching among thecontrol systems, the invention is not limited thereto. For example, theoperator may manually operate a switch in the pressing work so as toswitch among the control systems.

INDUSTRIAL APPLICABILITY

As will be seen from the above descriptions, according to the presentinvention, when the rotating body is in the stopped state, themechanical brake is actuated to hold the stopped body. The current tohold the body on the spot does not need to be constantly passed throughthe electric motor, which current might be necessary in the case ofstopping and holding the body only by the position holding control,thereby achieving energy savings. Additionally, in a boundary of thespeed control range, the position holding control is carried out,thereby eliminating the risk of excessive wearing of the brake, whichrisk might occur in the case of decelerating and stopping the rotationonly by the mechanical brake, while obtaining smooth accelerating anddecelerating effect without shocks caused by the operation ON/OFF of themechanical brake in the acceleration and deceleration of rotation, thusimproving the operability of rotation.

Further, the on-the-spot holding torque generated when performing theposition holding control in the neutral range is stored. The higher ofthe stored on-the-spot holding torque and the accelerating torqueaccording to the operation amount of the operation means is set as theelectric motor torque for acceleration when starting the rotation. Withthis arrangement, especially when the rotating body starts to rotatetoward an upper end side of an inclined ground or when the rotating bodystarts to rotate upwind under strong wind, the risk of the retrogrademotion of the rotating body is eliminated, thus resulting in improvementof the operability of the rotation.

Moreover, when performing the pressing work, instead of the speedcontrol depending on the operation amount of the operation means, thetorque control is carried out according to the operation amount, orcontrol including the speed control with torque limitation imposedthereon is carried out. In the pressing work, the rotation torque iscapable of being controlled through the use of the operation meansaccording to the operator's intentions, thereby improving theoperability in the pressing work.

1. A rotation control device for a working machine, the devicecomprising: an electric motor for rotatably driving a rotating body;operation means for issuing a rotation command for rotation of therotating body; control means for controlling said electric motor basedon the rotation command issued from said operation means; a rotatingspeed detecting means for detecting a rotating speed of the rotatingbody; and a mechanical brake for generating mechanical braking force,wherein said control means has a neutral range set by adding apredetermined width to an absolute neutral point serving as a basicpoint, the absolute neutral point corresponding to an operation amountof said operation means of zero, and in said neutral range, a mechanicalbrake zone is set on the absolute neutral point side, while a positionholding control zone is set on a side opposite to said neutral pointside, and wherein said control means is adapted to cause said mechanicalbrake to work in the mechanical brake zone of said neutral range, toperform position holding control in said position holding control zone,thereby stopping and holding said rotating body, and to perform speedcontrol according to the operation amount of said operation meansoutside the neutral range.
 2. The rotation control device for theworking machine according to claim 1, wherein a simultaneous use zonewhere the mechanical brake zone and the position holding control zoneare partially superimposed on each other is set in the neutral range,and wherein said control means causes both functions of the mechanicalbrake and the position holding control to be carried out in thesimultaneous use zone.
 3. The rotation control device for the workingmachine according to claim 1, wherein, in decelerating rotation, whenthe operation amount of the operation means is within said positionholding control zone and the rotating speed is equal to or less than apreset starting speed of a speed when the position holding controlstarts, said control means starts to perform the position holdingcontrol.
 4. The rotation control device for the working machineaccording to claim 1, wherein, in decelerating rotation, when theoperation amount of the operation means is within said mechanical brakezone and a condition in which the rotating speed is equal to or lessthan a preset brake operating speed continues for a set period of time,said control means actuates the mechanical brake.
 5. A rotation controldevice for a working machine, the device comprising: an electric motorfor rotatably driving a rotating body; operation means for issuing arotation command for rotation of the rotating body; control means forcontrolling said electric motor based on the rotation command issuedfrom said operation means; and a rotating speed detecting means fordetecting a rotating speed of the rotating body, said control meansperforming speed control according to an operation amount of saidoperation means and imposing a limitation on a maximum value ofaccelerating torque according to said operation amount, wherein, whensaid operation means is positioned within a preset neutral range, saidcontrol means is adapted to perform position holding control of saidrotating body, to store torque generated in said electric motor by theposition holding control as on-the-spot holding torque, and to set, inaccelerating the rotation, the higher of said on-the-spot holding torquestored and said accelerating torque produced according to the operationamount of said operation means, as electric motor torque foracceleration.
 6. The rotation control device for the working machineaccording to claim 5, wherein, in decelerating the rotation, saidcontrol means calculates braking torque according to the operationamount of said operation means based on preset braking torquecharacteristics, and sets the higher of said calculated braking torqueand said on-the-spot holding torque stored, as electric motor torque fordeceleration.
 7. The rotation control device for the working machineaccording to claim 5, wherein, when the operation means is returnedwithin the neutral range and the position holding control is performed,said control means restores the on-the-spot holding torque stored to aninitial value.
 8. The rotation control device for the working machineaccording to claim 5, further including a mechanical brake forgenerating mechanical braking force, wherein, when the operation mean ispositioned in a mechanical brake zone which is a part of the neutralrange and includes an absolute neutral point, said control meansactuates said mechanical brake.
 9. A rotation control device for aworking machine, the device comprising: an electric motor for rotatablydriving a rotating body; operation means for issuing a rotation commandfor rotation of the rotating body; control means for controlling saidelectric motor based on the rotation command issued from said operationmeans; and rotating speed detecting means for detecting a rotating speedof the rotating body, said control means performing speed controlaccording to an operation amount of said operation means, wherein, whenperforming a pressing work including pressing a part of said rotatingbody against an object of work, said control means performs torquecontrol according to the operation amount of said operation meansinstead of said speed control.
 10. A rotation control device for aworking machine, the device comprising: an electric motor for rotatablydriving a rotating body; operation means for issuing a rotation commandfor rotation of the rotating body; control means for controlling saidelectric motor based on the rotation command issued from said operationmeans; and a rotating speed detecting means for detecting a rotatingspeed of the rotating body, said control means performing speed controlaccording to an operation amount of said operation means, wherein, whenperforming a pressing work including pressing a part of said rotatingbody against an object of work, said control means performs control toimpose a torque limitation according to the operation amount of theoperation means on said speed control.
 11. The rotation control devicefor the working machine according to claim 9, wherein, in a conditionthe operation amount of said operation means is larger than an operationamount thereof at a starting position of the rotation and an actuallymeasured value of the rotating speed is zero, or is equal to or lessthan a set value near zero, said control means judges the condition thepressing work.
 12. A rotation control device of a working machine, thedevice comprising: an electric motor for rotatably driving a rotatingbody; operation means for issuing a rotation command for rotation of therotating body; control means for controlling said electric motor basedon the rotation command issued from said operation means; and a rotatingspeed detecting means for detecting a rotating speed of the rotatingbody, said control means performing speed control according to anoperation amount of said operation means, wherein, when an actuallymeasured value of the rotating speed is smaller than a target valuecorresponding to the operation amount of said operation means, saidcontrol means performs control to impose a torque limitation on saidspeed control.
 13. The rotation control device for the working machineaccording to claim 9, wherein, under condition that the operation meansis located at the starting position of the rotation, a target torque isset to be above zero.
 14. The rotation control device for the workingmachine according to claim 10, wherein, in a condition the operationamount of said operation means is larger than an operation amountthereof at a starting position of the rotation and an actually measuredvalue of the rotating speed is zero, or is equal to or less than a setvalue near zero, said control means judges the condition the pressingwork.
 15. The rotation control device for the working machine accordingto claim 10, wherein, under condition that the operation means islocated at the starting position of the rotation, a target torque is setto be above zero.
 16. The rotation control device for the workingmachine according to claim 11, wherein, under condition that theoperation means is located at the starting position of the rotation, atarget torque is set to be above zero.
 17. The rotation control devicefor the working machine according to claim 12, wherein, under conditionthat the operation means is located at the starting position of therotation, a target torque is set to be above zero.
 18. The rotationcontrol device for the working machine according to claim 14, wherein,under condition that the operation means is located at the startingposition of the rotation, a target torque is set to be above zero.